Heaters or furnaces are commonly used to heat fluid, such as air, circulated through a building to heat its interior. Some heaters burn solid fuel, such as wood or coal. Such heaters generally include a fire box in which the fuel is burned. Air is circulated to and from the heater via a duct system generally including a cold air duct and a hot air duct communicating with the building. The heater receives air from the building via the cold air duct. The air is heated as it flows over the fire box in a heat exchanger portion of the heater. The heated air is returned to the building via the hot air duct to heat the interior of the building.
Conventional heaters of this type include electrical components used for regulating the heater. One such electrical component is a main electrical control used to control overall operation of the heater. Other electrical components include a blower for circulating air within the heater to move the air over the fire box and a blower limit switch turning the blower on when temperature in the heater exceeds a predetermined threshold.
In various circumstances, the heater may become too hot, potentially damaging the heater, including its electrical components, and ultimately the duct system and the building. The excessively heated air may result from the electrical components losing power or malfunctioning. For example, if the blower malfunctions, air may not be blown over the fire box, resulting in heat buildup inside the heater. To prevent damage, it is desirable to automatically “dump” or release excessively heated air from the heater.
Some heaters include automatic systems for releasing hot air when overheating. In one prior art heater, a thermal sensor and a heat dump opening are provided to release hot air from the hot air duct when temperature in the duct exceeds a predetermined value.